Trunnions and Modularity in Total Hip Arthroplasty: A Historical Review With Current Clinical Implications

Abstract

Trunnion in total hip arthroplasty refers to the interface between the neck of a femoral stem and the femoral head. Clinical complications arising from damage to this junction, whether it be due to mechanical wear, corrosion, or a combination, are referred to as mechanically assisted crevice corrosion (MACC), also commonly known as trunnionosis. With the use of modular hip prostheses, which help customize offset and leg length to an individual patient's anatomy, the incidence of MACC and revision due to MACC has increased in recent years. Although the cause of MACC is multifactorial, with patient factors and technique factors contributing to this condition, taper design and geometry, metallurgical properties of implants, and size mismatch of the bearing couple are some of the implant factors that have also been implicated in this clinical phenomenon. Understanding the history of taper design and geometry, the track record of older implants, and the rationale behind the development of current prostheses can help surgeons choose the right implants for their patients and accurately assess the pros and cons of new implants being introduced to the market each year. Charnley 1 became the father of the modern total hip arthroplasty (THA) when he introduced his low-friction design in 1961. He used acrylic cement to fix metal to live bone, polyethylene as a bearing surface, and monoblock femoral implant with a small head for low frictional torque. Introduction of modularity allowed the separation of Charnley monoblock femoral implant into the femoral stem and femoral head. This allowed fine-tuning of the femoral offset and leg length independent of the femoral stem size, thus facilitating customization of the implant to the individual's anatomy. 2 However, modularity comes with its own risks and disadvantages, and understanding these can help the orthopaedic surgeon decrease the risk of complications after THA.

Analysis of modular taper fractures of the revision hip stem Prevision and comparison of the original and current taper design

“…There were no cases of failure of the modular taper by other patterns such as modular taper loosening or taper corrosion. 21 In the analysis, no correlation was observed to distal stem length or diameter, or to proximal component size.…”

Trunnionosis in metal-on-polyethylene total hip arthroplasties: Report two cases

“…Patient-related factors could also play a role in the incidence of trunnionosis. For example, the immune response to corrosion products is different between the patients [ 17 , 18 ]. Hallab et alanalyzed the immune response of THA patients to implant metals compared to different control groups.…”